Etiam tu, mi fili Brute?

also it was "tu quoque brute"

Not in the play by Shakespeare it wasn't, it was indeed "et tu, Brute?".
Some people think he spoke a Greek sentence, which would have been that in Latin, only with "my child" (or "fili mi") on the end as well, which is where some speculation about Brutus being Caesar's son comes from.

Though the view of the historian whose works this information came from said himself that Caesar was silent as he died, all quotes were claims of others he merely mentioned.
Though, of course, because of the way generals/emperors/et cetera were treated and thought of, we can't be sure of very much information at all.

Brutus is the guy who Ceasar saw as his best friend, ''et tu Brutus?'' was what he said after everybody including Brutus betrayed him.



******* .

Latin nouns decline depending on the grammatical role. Brutus is the nominative form. Being a subject. But Brute is its vocative form, when it is being addressed.

In the play by Shakespeare, which is where this phrase is from, it's written as Brute.

Latin noun endings change to fit their purpose
the name "Brutus" is given in English in it's nominative form
when spoken to directly, nouns take the vocative ending
which, for the second declension, is -e

******* .

You seem to be right sir, excuse me. =]